Gas-filled overvoltage diverter

ABSTRACT

In a gas-filled overvoltage diverter, the electrodes are coated with an activation compound and are located on an insulator. At least one axial ignition strip is disposed on the inner surface of the insulator. The inner surface of the insulator also has an ionization source in the form of a coating of an electroluminescent material. The coating is connected to both electrodes and may take the form of a strip. Alternatively, the coating may cover the entire inner surface of the insulator. The alkali halide and/or alkaline-earth halide coating material may also contain dielectric or ferro-electric crystals.

FIELD OF THE INVENTION

The invention is in the field of electronic components. Morespecifically, the invention is used in the construction of gas-filledovervoltage diverters. To ensure the ignition properties, the electrodesof the gas-filled overvoltage diverters are coated with an activationcompound, and at least one axially running ignition strip and anadditional ionization source are applied on the wall of the insulatingbody.

BACKGROUND OF INVENTION

Overvoltage diverters filled with inert gas have a number of desiredperformance characteristics including: igniting voltage, response time,static response voltage, dynamic response voltage, extinction voltageand glow operating voltage. To achieve each of these desired performancecharacteristics, different measures like the constructive design of theelectrodes, the type and pressure of the gas filling, and the selectionof the activation compound arranged on the active surfaces of theelectrodes must be adjusted to one another. Furthermore, to producedefinitive ignition conditions, one or more ignition strips arecustomarily arranged on the inside wall of the glass or ceramicinsulator and a special ionization source may also be provided. Forexample, a known overvoltage diverter has two electrodes inserted intothe two front ends of a ceramic insulator; the electrode surfaces faceeach other and are coated with an activation compound in depressions inthe electrode surface. A plurality of ignition strips running in theaxial direction of the ceramic insulator are arranged on the insidewall. The ignition strips are called middle ignition strips because theydo not directly interface with the electrodes as described in U.S. Pat.No. 4,266,260 and German Patent 28 28 650.

Furthermore, where gas-filled overvoltage diverters are arranged in aspace shut off from outside light influence during their operation, anadditional ionization source in the form of a point-shaped deposit of aradioactive material is customarily arranged on the inside wall of theinsulator. Alternatively, the gas filling of the overvoltage divertercan consist of a radioactive gas as shown in U.S. Pat. No. 3,755,715.

SUMMARY OF THE INVENTION

The invention seeks to develop an overvoltage diverter that exhibitsvery slight ignition delay in the dark space, even without the use of aradioactive preparation.

The invention achieves this objective by another ionization source, inaddition to the two electrodes, which comprises a coating connecting thetwo electrodes. The coating is made of an electroluminescent materialbased on alkali halides and/or alkaline-earth halides where the coatinghas a thickness of approximately 50 to 500 μm.

For example, potassium bromide and sodium bromide, potassium chlorideand sodium chloride, and sodium fluoride and barium chloride can be usedfor the coating as described in (Opt. Spectrosc. (USSR) 51 (2), Aug.,1981, Pages 165-168). As parent substances, alkali-fluorides andalkali-bromides are to be particularly considered because theyadditionally contain alkaline-earth chloride. The additionalalkaline-earth halide should be in a quantity of 5%-30% atomicpercentage. Because of this additional alkaline-earth halide, themelting process necessary to apply the coating can be specificallycontrolled with regard to the melting temperature.

Because the coating contacts the two electrodes of the overvoltagediverter, the coating places an increased number of primary chargecarriers at disposal in the overvoltage diverter so that, upon reachingthe igniting voltage, the start of the gas discharge is initiatedwithout time delay. Additionally, to strengthen this effect, the coatingmaterial can contain dielectric crystals (e.g., titanium oxide oraluminum oxide) or ferro-electric crystals (e.g., barium titanate,lithium niobate or lithium tantalate). Because such crystals have aparticle size of approximately 10-30 μm, an increased charge density isproduced at their interface resulting in a higher current flow in theelectroluminescent coating and, consequently, in a higher photon yield.

In the simplest case, the electroluminescent coating is applied asstrips along the center line of the insulator. One such strip can havethe width of 1 to 5 mm. At the same time, the strip-shaped coating cancover the ignition strip or ignition strips provided on the inside wallof the insulator. Alternatively, a plurality of strip-shaped coatingscan be arranged alternately with a plurality of ignition strips.Optionally, the entire inner surface of the insulator can also beprovided with the coating.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overvoltage diverter with a coating applied inside onthe insulator.

FIG. 2 shows in cutaway portions the development of the inner surface ofa ceramic insulator which is coated alternately with ignition strips andluminescent strips FIG. 3 shows a coating enriched with crystals.

DETAILED DESCRIPTION

The overvoltage diverter according to FIG. 1 consists of two bowl-likeelectrodes 1 and 2 which are soldered at the two front ends into theceramic insulator 3. The active surfaces of the electrodes 1 and 2 arecoated with an activation compound 4 which is embedded in shallowdepressions in the electrodes. This activation compound is a customarycompound based on alkali halides or alkaline-earth halides having ametallic additive such as a barium aluminum alloy, titanium, molybdenumand/or nickel.

The overvoltage diverter is provided with a gas 5 based on argon and/orneon, possibly with an addition of hydrogen.

Graphite ignition strips 6 are applied on the inside wall of theinsulator 3; the strips are called middle ignition strips because theydo not interface with either of the two electrodes. Furthermore, theinside wall of the ceramic insulator is provided with a coating 9 madeof an electroluminescent material which contacts the two electrodes 1and 2.

As shown in FIG. 3, crystals 8 can be embedded in the coating 9.

As shown in FIG. 2, a complete coating of the inner surface of theceramic insulator 3 can be substituted with a strip-shaped coating 9alternately arranged with ignition strips 6. For example, two or fourignition strips 6 and two or four strip-shaped coatings 9 can bepresent.

The application of the coatings 9 is accomplished by applying a pasty,aqueous solution of, for example, sodium fluoride with an addition ofbarium chloride (for example, 1 g=0.024 Mol NaF; 1.25 g=0.006 Mol BaCl₂)and by a heat treatment, for example, in the course of the soldering ofthe electrodes into the ceramic insulator. The heat treatment bringsabout a fusing of the coating material; this fusing is necessary for thelater effectiveness of the coating.

We claim:
 1. A gas-filled overvoltage diverter, comprising:a hollowcylindrical insulator having a first frontend, a second front end and aninner surface; a first electrode arranged at said first front end ofsaid insulator and coated with an activation compound; a secondelectrode arranged at said second front end of said insulator and coatedwith said activation compound; plurality of axially running ignitionstrips made of graphite applied on said inner surface of said insulator;and a plurality of coating strips applied on said inner surface of saidinsulator alternating with said plurality of ignition strips, eachcoating strip connecting said first electrode and said second electrodeand being an ionization source, each coating strip being made of anelectroluminescent material based on alkali halides, alkaline-earthhalides, or a combination of alkali halides and alkaline-earth halidessaid plurality of coating strips having a thickness of approximately 50to 500 μm.
 2. The gas-filled overvoltage diverter of claim 1, whereineach coating strip includes alkali-fluorides, alkali-bromides or acombination of alkalifluorides and alkali-bromides as a parent substancewith an addition of an alkaline-earth chloride.
 3. The gas-filledovervoltage diverter of claim 2, wherein each coating strip includessodium fluoride with an addition of barium chloride.
 4. The overvoltagediverter of claim 3, wherein each coating strip is a material containinga plurality of dielectric or ferro-electric crystals.
 5. The overvoltagediverter of claim 1, wherein each coating strip is a material containinga plurality of dielectric or ferro-electric crystals.
 6. The overvoltagediverter of claim 2, wherein each coating strip is a material containinga plurality of dielectric or ferro-electric crystals.